Pulp screen



Oct. 10, 1950 w. F. MATHEWSON 2,525,701 4 PULP SCREEN Filed Dec. 10, 1948 5 Sheets-Sheet 2 INVENTOR. W/L FR ED 5 MA T/{EWSON M M aim A TTORNE Y5.

patented Oct. 10,

UNITED STATES PATENT OFFICE 2,525,701 PULP SCREEN Wilfred F. Mathewson, Boston, Mass, assignor-td Mathewson Machine Works, Inc., Quincy, Mass, a corporation of Massachusetts Application Decemher ltl, 1948, Serial-No; 64,539-

3 Claims.

This invention relatesto, pulp. screens of the type shown in my U. S; Patent. No. 2,450,838, October 5, 1948.

The pulp screen illustrated in saidpatent comprises a casing having aninlet for the. unscreened pulp and an outlet". for the screened. pulp, and pulp-screening means within the casing comprising two concentric substantially cylindricalscreen members providing between. them an annular clearance space ofsufiicient size for the fine acceptable portion of the unscreened pulp to pass therethrough, but of insufficient size .for the coarse unacceptable portion of such pulp to pass therethrough. One of the screen. members is formed on its face which. bounds the clearance space with a plurality of slots or grooves which extend parallel to the axis. of the concentric screen members, certain of which slots constitute inlet slots-and have communication. with the inlet to the casing while the remaining slots. constitute discharge slots and have communication with the outlet for thescreened. pulp. Each of these slots have parallel walls and they are situated closely adjacent. each other, thealternate slots being inlet slots so thateach inlet slot has.

a discharge slot on each side thereof.

In the operation of screening the pulp, the unscreened pulp which is delivered through the in.-

let oi" the casing. flows into the inlet slots andfrom the latter. intothe clearance space; the ace: ceptable portion of the pulp which enters each.

inlet slot flowing through the clearance space and into the discharge slots on either side of the inlet slot, from which discharge slots the screened;

pulp is delivered through the outlet to the casing. While the clearance space is of a size to permit the acceptable portion of the pulp to pass therethrough, yet its size is insufiicient to permit shives and other coarse unacceptableportions of the pulp to pass.

In order to prevent such unacceptable portion of the pulp from clogging the screen, the nonslotted screen element is provided with ,aplur-ality of openings, and one of the screen elements is rotated relative to the other about their; common axis so that when. during such a relative rotation, any coarse unacceptable portion of the pulp which is unable to pass through. the clearance spaces comes intcregister with one of the openings, such unacceptable portion will be flushed. through the opening, thus clearing the screen.

element.

In the device of the above-mentionedpatent, the walls or ribs which. separate the. various grooves have flat faces and each wall presents two sharp corners at. the edgen thereof adjacent. the. clearancespace, around'whichthe acceptable portion of; the pulp. must fiowin traveling from an inlet slot through the; clearance. space into an outlet or. discharge. slot. It has: been found. that in flowing from. an. inlet slot: into a. discharge. slot through. the clearance; space, .a fiber of pulp stock which of itself would be classified as acceptahle. sometimesggetsi caught. on one of the sharp corners of the wall instead. of flowing freely through. the) clearance space, and when this. happensanother acceptable. fiber i likely to. clingto the,blockedacceptable-fiber and thereby. a. clot or acceptable fibersmaybe built up at the point where the inlet-s slot opens into the clearance; space, which: clot forms an obstruction to the flow of acceptable fiberwthrough the clearance space-inthesame manner as would be produced by the. blockingof the passage by the unacceptable portion of the, pulp. If. such a blockade or clot of acceptable. portion of the pulp is formed, then. as thescreen. members rotate relative' to each other such blockade of acceptable portionqwillbe flushedoutthrough the opening in the non-slotted member. and will be added. to the tailings. onaunacceptable portion of the pulp. This, of course,. constitutes a needless waste of good material.

Itis one of the objects of the present invention to provide; an improved. pulp screen of the above;.type whiclnis soconstructed as to reduce to a minimum, .oreven to practically. eliminate, the possibility oi any blockade or. clot. of acceptable portionoithe stock developinginthe clearance space, thereby providing a screen which;Willyield ahigher percentage of screened pulp from a given quantity of unscreenedpulp.

Other objects-lot the invention are to improve pulp screens of the above type in the particulars hereinafter set=.forth-.

I have illustrated the present invention as it might beqembodied, in a. laboratory. type pulp screen I rather. than. a full sized commercial Fig; 3-1is anzenlarged fragmentary view of the:

operative portions of .the :two screen elements.

Fig. 4 is a, fragmentary sectional view on the line 4+4, ,Figa.

i ig. is a view illustrating a laboratory type screen embodying the features shown in the other figures of the drawings.

My improved screen comprises a casing element i which is formed with an annular inlet chamber 2 to which the unscreened pulp is delivered and with an annular discharge chamber into which the screened pulp is delivered after having passed through the screening elements, said discharge chamber 3 having an outlet a to which a discharge pipe 48 may be connected (see Fig. 5). The unscreened pulp may be fed to the annular inlet chamber 2 in any suitable way, such as an inlet pipe ll leading to an inlet opening 42.

The two screen elements are indicated at 5 and 6 respectively. These two elements are substantially cylindrical and are arranged concentric with each other, the element 5 constituting the outer screen element, and the element 6 constituting the inner screen element.

Said screen elements are so constructed that there exists between them an annular clearance space 'E which is of a size to permit the fine acceptable portion of the pulp to pass therethrough but which is insufi'icient in size to permit the coarse unacceptable portion of the pulp to pass.

In the present embodiment of the invention, the outer screen member 5 is a stationary member and is stationarily mounted within the easing in such a way as to form between itself and the casing the annular inlet chamber 2. The inner screen member 6 is a rotary member, and it is shown as mounted on a shaft 8 which is 'ournaled in the casing for rotative movement.

The stationary screen member 5 is formed with a series of vertical slots i3 which extend radially therethrough and which thus communicate with both the surrounding inlet chamber 2 and the annular clearance space i. Said slots 9 thus constitute passages through which the unscreened pulp ilows from the inlet chamber 2 into the clearanc space and are therefore referred to as inlet slots.

The screen member 5 is also provided with second series of slots H] which are parallel to the slots i and which communicate with the clearance space i but have no communication with the inlet chamber the clearance space. These slots Iii extend through the upper end of the screen member 5 and open into the discharge chamber 3 as shown at is in Fig. 4 and hence. are referred to as discharge slots.

The slots 9 and it are so arranged that they alternate with each other, every other slot being an inlet slot and hence each inlet slot 9 has a discharge slot iii on each side thereof, the adjacent slots being separated by walls or partitions l i.

In the present embodiment of my invention, each inlet slot 9 has a progressively decreasing width from its outer inlet side E2 to its inner delivery side 53 as best seen in Figs. 2 and 3, and is narrowest at the point Where said slot communicates with the clearance space. Furthermore the partition walls 5 l are made with rounded corners M on the sides thereof which bound the inlet slots 9 as best seen in Fig. 3.

During the screening of the stock the unscreened stock which flows inwardly through each inlet slot 9 as shown by the arrows a in Fig. 3 will divide as it flows into the clearance space i as indicated by the arrows 1), part of 2 except through such stock flowing around the Wall H on one side of the inlet slot into the adjacent discharge slot l6, and the other part flowing around the wall ii on the other side of the inlet slot into the corresponding discharge slot it. The converging or tapered shape of the inlet slots 9 tends to cause pulp to flow with an increased velocity through the clearance space and around the walls ii, and the rounded corners E4 of the walls serve to facilitate such flow and tend also to reduc materially the possibility of any pulp fiber of an acceptable size and length from being caught in the clearance space.

Of course any large coarse unacceptable portion of the pulp stock which cannot pass through the clearance space T will become lodged or blockaded at the entrance to the clearance space.

For flushing out such blocked or lodged portions of pulp, the inner screen member 6 is made with an interior chamber [5 and is provided with a pluralit of flushing openings IB which lead into said chamber. These openings in are in the nature of elongated slots as shown in Fig. 1. When during the rotation of the inner screen member 8 any flushing slot l 6 comes into register with any portion of pulp which has been blockaded at the clearance space, such blockaded portion of the pulp will be flushed through the slot l6 and into the interior chamber it in which the tailings collect.

The casing i is provided with a tailings outlet H which communicates with a chamber l8 that in turn opens into the interior chamber ii of the inner screen member. There is provided a tube is which extends from the chamber l8 nearly to the top of the chamber l5 so that any tailings or unacceptable pulp which flows through the slots I 6 into the chamber i5 is required to flow over the top of the tube [9 in order to be delivered from the casing.

The unscreened puip may be delivered to the inlet cylinder 2 in any suitable way, and there is shown for this purpose a supply pipe it communicating with an inlet opening 52 leading to the inlet chamber 2.

The drawings show the pulp screen as it might be embodied in a laboratory model, but the embodiment of the novel features in a full sized commercial machine merely involves making them on a larger scale than is found in the laboratory model.

In the device shown herein the shaft 8 by which the rotary screening element 6 is rotated is driven from a motor 25 through suitable reduction gears contained in a casing 26, the power output shait 2? of the reduction gears being connected to the shaft 8 through suitable universal joint connection 28.

The outlet pipe 46 for the screened pulp is shown as connected to the inlet of a pump 29 which assists in maintaining a flow of the pulp through the pulp screen.

The pump is of the rotary type and is driven from the shaft 2? through a belt 36 extending around a driving pulley 32 on a shaft 2'! and a driven pulley 38 on the shaft of the pump.

The outlet H for the tailings leads into a discharge pipe 38 and there is shown another pump 33 in the pipe 36 for maintaining circulation therethrough. This pump 33 is also driven from the shaft 27 through the medium of a driving belt 34 and pulleys 35 and 36.

I claim:

1. A pulp screen comprising a casing, two concentric screen elements located therein and forum ing between them an annular clearance space of suflicient size for the passage therethrough of the acceptable portion of the pulp but of insufiicient size for the coarse unacceptable portion of the pulp to pass therethrough, said casing and the outer screen element forming between them both an annular inlet chamber and a discharge chamber, said outer screen element having a plurality of radially arranged spaced partition members forming between them slots, all of which slots communicate with the clearance space, the alternate slots also communicating with the inlet chamber and constituting inlet slots and the remaining slots communicating with the discharge chamber and constituting discharge slots, each partition presenting a rounded corner at the junction of the corresponding inlet slot and the clearance space over which the acceptable portion of the pulp flows smoothly into the clearance space and from thence to a discharge slot, thereby reducing the possibility of the clearance space becoming clogged by acceptable portion of the pulp.

2. A pulp screen comprising a casing, two concentric screen elements located therein and forming between them an annular clearance space of sufiicient size for the acceptable portion of the pulp to pass therethrough but of insufiicient size for the coarse unacceptable portion of the pulp to pass therethrough, said casing and the outer screen element forming between them both an annular inlet chamber and a discharge chamber, said outer screen element having a plurality of inlet slots forming a communication between the inlet chamber and said clearance space and also having a plurality of discharge slots communicating both with the clearance space and with the discharge chamber, said inlet and discharge slots alternating in position and each inlet slot having a progressively decreasing width from the inlet chamber to the clearance space and being narrowest at the place where it opens into said clearance space, whereby the accelerated flow of the pulp as it passes into the clearance space from each inlet slot resulting from the progressive decrease in the width of the slot minimizes the possibility of the clearance space becoming clogged by acceptable portion of the pulp.

3. A pulp screen comprising a casing, two concentric screen elements located therein and forming between them an annular clearance space'of suilicient size for the acceptable portion of the pulp to pass therethrough but of insufficient size for the coarse unacceptable portion of the pulp to pass therethrough, said casing and the outer screen element forming between them both an annular inlet chamber and a discharge chamber, said outer screen element having a plurality of radially arranged spaced partition members forming between them slots, all of which slots communicate with the clearance space, the alternate slots also communicating with the inlet chamber and constituting inlet slots and the remaining slots communicating with the discharge chamber and constituting discharge slots, the walls of each inlet slot being non-parallel and having a converging relation from the inlet chamber to the clearance space, the distance between the walls of each inlet slot being least where said slot opens into the clearance space, each partition presenting a rounded corner at the junction of the corresponding inlet slot and the clearance space, whereby the accelerated movement of the pulp as it leaves each inlet slot due to the convergence of the walls of the slot, together with said rounded corners, reduces to a minimum the possibility that the clearance space will become clogged by acceptable portion of the pulp.

WILFRED F. MATHEW SON.

REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,964,291 Kutter June 26, 1934 2,275,776 Lane et a1 Mar. 10, 1942 2,450,838 Mathewson Oct. 5, 1948 

